The present disclosure generally relates to design of a structured light pattern, and specifically relates to generating a tileable structured light projection for wide field-of-view (FOV) depth sensing.
Current solutions for achieving structured light illumination with a wide FOV for depth sensing include an approach based on a single wide FOV diffractive optical element (DOE), an approach based on a dual DOE, and an approach based on tiling multiple projectors with projection distortion. However, each of these solutions has its own disadvantages. For example, the approach based on a single wide FOV DOE suffers a relative large zero-order value compared to other diffraction orders. The large zero-order value can lead to issues in laser safety compliance and algorithm performance. Also, the large pincushion like distortion in the light projection causes inefficient use of a projector power. For the approach based on the single DOE for achieving wide FOV, the zero-order value is largely limited by a process error, such as the depth etching error. For example, a depth etching error of 2% leads to a zero-order value of approximately 0.1%. Achieving lower zero-order values than 0.1% based on the single wide FOV DOE means low yield and high price for fabricating a DOE.
The approach based on dual DOE that utilizes a tile DOE and a tiler DOE can further reduce the zero-order value by tiling a light pattern generated by the tile DOE to fill the entire FOV. The zero-order value of the tile DOE can be effectively reduced by a factor equal to a number of tiling projections. For example, 3×3 tiling provides effective reduction of the zero-order value by the factor of nine. However, the approach based on dual DOE increases the DOE complexity and cost, while still having an issue with pincushion distortion. The approach based on dual DOE also restricts the space of achievable pattern to the one that repeats across the field which results in additional algorithmic complexity.
The DOE-based structured light projection suffers intrinsic distortion (i.e., the pincushion like distortion) due to the law of diffraction, which increases rapidly as FOV increases. The intrinsic distortion causes overlapping of light patterns and/or voids (i.e., gaps in light patterns) when tiling multiple light projections to achieve wider FOV illumination, which leads to increased complexity of depth sensing algorithms and less efficient use of a projector power. A simple tileable projection shape is a rectangular or square shape. For achieving such a rectangular or square shape of light projection, the rectangular design pattern can be shaped on finer grids (e.g., each grid corresponding to a diffraction order) such that the projected light pattern exhibits desired rectangular shape after illuminating a DOE designed with the re-shaped rectangular light pattern. However, the distortion pre-compensation approach uses more diffraction orders in DOE design and demands more advanced fabrication process, leading to a higher price.